This is a sample clock application using STM32 RTC capability and an external I2C LCD.
Note: PB8 and PB9 pins are 5V-tolerant as per the datasheet.
Use terminal emulator such as Teraterm to open the COM port.
If the current date and time is "May 2, 2018" on Tuesday, then the command is like this:
18 5 2 16 25 2[LF]
Push the user button (blue button) on the Nucleo board to show the date and time on the terminal emulator.
This application output date and time to LCD every 30 seconds.